The present invention is generally directed to vision and treatment of the eye to provide improved vision. Although specific reference is made to coverings for vision correction such as the correction of refractive error and also to treatment of eyes having epithelial defects following photorefractive keratectomy, embodiments of the present invention may comprise extended wear contact lenses that can be used to correct vision in many ways such as with one or more of aberration correction, multifocal correction, presbyopia correction, and astigmatism correction.
The eye includes several tissues that allow patients to see. The cornea of the eye is an anterior tissue of the eye that is clear in healthy eyes and refracts light so as to form an image on the retina. The retina is a posterior tissue of the eye that senses light from the image formed thereon and transmits signals from the image to the brain. The cornea includes an outer layer of tissue, the epithelium, which protects the underlying tissues of the cornea, such as Bowman's membrane, the stroma and nerve fibers that extend into the stroma and Bowman's membrane. The healthy eye includes a tear film disposed over the epithelium. The tear film can smooth small irregularities of the epithelium so as to provide an optically smooth surface. The tear film is shaped substantially by the shape of the underlying epithelium, stroma, and Bowman's membrane, if present. The tear film comprises a liquid that is mostly water and does include additional components, such as mucoids and lipids. The many nerve fibers of the cornea provide sensation to promote blinking that can cover the cornea with the tear film. The nerve fibers also sense pain so that one will normally avoid trauma to the cornea and also avoid direct contact of an object to the cornea so as to protect this important tissue.
Work in relation to embodiments of the present invention suggests that at least some of the prior contact lenses and therapeutic coverings can be less than ideal in at least some instances. Many contact lenses and therapeutic coverings can be left in the eye for less than ideal amounts of time, as the patient removing and replacing the contact lens or therapeutic covering can be somewhat cumbersome and in at least some instances patients may leave the contact lens or therapeutic covering in the eye for amounts of time that can be longer than would be ideal. Although extended wear lenses can be left in the eye for somewhat longer amounts of time, the amount of time such lenses can be left in the eye can be less than ideal. Work in relation to embodiments of the present invention also suggests that tear flow of the prior contact lenses can be less than ideal, and that less than ideal tear flow may be related to the potential complications and can limit the amount of time such lenses can be left in the eye.
In the healthy cornea, the proper amount of hydration of the cornea, sometimes referred to as dehydration of the cornea, is maintained such that the cornea remains clear. The cornea includes a posterior endothelial layer that pumps water from the cornea into the adjacent anterior chamber. The epithelium inhibits flow of water from the tear liquid into the cornea, such that the corneal stroma can be maintained with the proper amount of hydration with endothelial pumping. The endothelial pumping of water from the cornea to maintain the proper hydration and thickness of the eye is often referred to as deturgescence. When the corneal epithelium heals, the layer of cells forming over the defect can be at least somewhat irregular in at least some instances, such that the vision of the patient can be less than ideal.
As the post-ablation cornea may have a complex shape, many of the prior commercially available lenses may not fit the ablated cornea as well as would be ideal, and in at least some instances fitting of lenses can be time consuming and awkward. Rigid gas permeable (hereinafter “RGP”) lenses can be uncomfortable for the patient and difficult to fit. Commercially available contact lenses having a rigid central portion and a soft peripheral skirt can be difficult and/or time consuming to fit to the ablated cornea and may not fit very well in at least some instances. The ablated cornea may comprise an abrupt change in curvature near the edge of the ablation, and in at least some instances it can be difficult to fit such lenses near the edge of the ablation. Also, at least some of the commercially available contact lenses may not be suitable for extended wear and may be removed each day, which can be somewhat awkward for a patient and can result in lack of compliance and lenses remaining in the eye longer than would be ideal in at least some instances.
In light of the above, it would be desirable to provide improved contact lenses for vision correction and coverings for treatments related to epithelial defects of the cornea, such as epithelial defects following photorefractive keratectomy (hereinafter “PRK”). Ideally, these contact lenses and coverings would provide treatments that improve tear flow and avoid at least some of the deficiencies of known techniques while providing improved patient comfort and/or vision.